Field of the Invention
The embodiments disclosed herein relate to a rotation controller for an AC electric motor and a method for controlling rotation of the AC electric motor.
Discussion of the Background
In order to control the rotation of IPM (Interior Permanent Magnet) motors or perform what is called vector control (field-oriented control) of AC electric motors, it is necessary to know the rotational angle (current position) of the rotor. A commonly known method to know the rotational angle of the rotor is to provide the rotor with a sensor to detect its rotational angle. Another method to know the rotational angle of the rotor is “sensor-less” technology, which is in development and utilizes information obtained from a rotation controller for an AC electric motor.
For example, Japanese Unexamined Patent Application Publication No. 2003-299381A1 discloses obtaining the rotational angle of the rotor of a motor in a high-speed rotation region of the motor using a state observer that uses a numerical-formula model of an AC electric motor. A commonly known method to know the rotational angle of the rotor in a low-speed rotation region of the motor is to superpose a high frequency over the output frequency of the electric motor and use a resulting response to know the rotational angle of the rotor.
Japanese Unexamined Patent Application Publication No. 8-205578A1 discloses a device for detecting the magnetic pole position of a motor that has an electrical saliency based on the amount of change of output current ripple of an inverter in a switching period of PWM control and based on the amount of change of a time integration value of output voltage.